As is well known to those skilled in the art, lubricating oil fractions recovered from atmospheric distillation or from vacuum distillation require further treatment before they can be used to formulate finished lubricating oils. The type and degree of treatment may vary depending on the composition of the fraction which may be derived, for example, from (i) a bright stock recovered as bottoms from vacuum distillation of a paraffinic crude or from (ii) a wax distillate recovered as a side cut from vacuum distillation of a paraffinic reduced crude or of an asphaltic reduced crude.
Further treatment of these lube oil stocks may include a wide variety of operations, such as dewaxing, solvent extraction, acid treatment, etc., to provide finished bright stocks or distillate lube oils.
Dewaxing, to remove wax from wax-bearing lube oil stocks, is carried out to provide a product which has improved cold weather properties, i.e. which does not precipitate wax under cold conditions, and which also may be characterized by improved viscosity, viscosity index, etc. MEK dewaxing is commonly carried out with a solvent containing toluene as the oil solvent and methyl ethyl ketone as the wax antisolvent.
It is important to control the ratio of MEK to toluene and to be able to adjust this ratio, since it allows utilization of the optimum concentrations for processing various base stocks. Commonly a ratio of 0.7:1 to 1:1, say 1 (i.e. 1:1) may be used when processing bright stocks; and a ratio of 1.2:1 to 2.3:1, say 2 (i.e. 2:1) may be used when processing light stocks.
Alternatively expressed, bright stock may be dewaxed with solvent typically ranging from 70:30 to 50:50, while light stock may utilize 40:60 to 50:50 methyl ethyl ketone: toluene ratios. These ratios are weight ratios.
Clearly an operator of a single train dewaxing operation finds it desirable to be able to process a full range of lube oil feed stocks in that train; but this has heretofore required substantial additional capital and operating expense to adjust the ratio, as by distillation.
It is an object of this invention to provide a novel process for treating a charge mixture containing a charge ratio of oil solvent and wax antisolvent to obtain a product mixture containing a different ratio of oil solvent and wax antisolvent. Other objects will be apparent to those skilled in the art.